Interactions between two biological control agents of Pereskia aculeate

Interactions between two biological control agents of Pereskia aculeateZezethu MNQETA1, Iain D. Paterson1, Steve Compton1,21Biological Control Research Group, Department of Zoology & Entomology, Rhodes University, Grahamstown, 6140 South Africa2School of Biology, University of Leeds, LS29JT, UK

Pereskia aculeata Miller (Cactaceae) is an alien invasive plant introduced into South Africa from Brazil. In South Africa, it is a problematic plant that has negative impacts on native biodiversity. Pereskia aculeata has two biocontrol agents, Phenrica guerini Bechyne (Chrysomelidae) and Catorhintha schaffneri Brailovsky & Garcia (Coreidae), released against it in South Africa. This study evaluated interactions between the agents, by investigating whether both agents, individually or jointly, enhanced or reduced the impact on P. aculeata. Potted P. aculeata plants were exposed to one of four treatments: control (no agents), P. guerini only, C. schaffneri only and both species in combination. Four stocking densities ranging from 2 to 12 insects per plant were used. Plant parameters including the change in number of leaves and change in shoot lengths were recorded. Catorhintha schaffneri alone at high densities was more damaging than other treatments with a significantly greater reduction in the number of leaves (-11.7 ± 1.29) and the shoot lengths (-2.17cm ± 0.75 cm) in this treatment. Even at lower density treatments, the combination of the two agents was not significantly more effective than C. schaffneri alone and C. schaffneri was always more effective than P. guerini alone. Mortality of P. guerini (14.7 ± 2.39) was significantly higher than C. schaffneri (6.20 ± 0.90) at all stocking densities when in combination. Catorhintha schaffneri should therefore be the priority species for further mass-rearing and releases on P. aculeata.